J . Am. Chem. SOC.1989, 1 1 1 , 2575-2580
2515
Transition Metal-Organoindium Chemistry. Addition of Alkyl-Indium Bonds to Alkyliridium Compounds and the Structure of IrH( Et)(Et21n)(PMeJ3 D. L. Thorn* and R. L. Harlow Contribution No. 482.5 from the E . I. du Pont de Nemours and Company, Central Research and Development Department, Experimental Station, P.O. Box 80328, Wilmington, Delaware 19880-0328. Received August 3, 1988
Abstract: Alkyl-indium bonds of bromodimethylindium, trimethylindium, and triethylindium add to the iridium compound (1,2), IrMe2(InMe2)(PMe3)3(3,4), and IrH(C2H5)(In(C2H5)2)(PMe3)3 IrMe(PMe3)4,and the products IrMe,(l~~MeBr)(pMe,)~ ( 5 ) have been isolated and characterized. The addition reaction of trimethylindium is reversed by exposure to excess trimethylphosphine or ethylene. For the triethylindium-hydridoiridium compound 5 an X-ray structure determination has been completed: space group P2,/n; a = 14.836 (3), b = 14.658 (3), c = 11.022 (2) A; p = 90.22 (1)'; Z = 4. An uncommon 3-coordinate organoindium entity is present in this compound. Dimethylzinc and IrMe(PMe3)4react analogously; reactions between alkylplatinum and alkylrhodium compounds and alkylindium compounds have been observed, but products have not been isolated.
Volatile organometallic compounds of the main-group metals have become profoundly important in the growth and processing of semiconductor devices. Critical to this application of alkylmetal compounds are reactions that cleave the metal-alkyl bond, removing the organic ligands from the metal atom and allowing it to assume its position on the growing surface of the desired material.' We became interested in whether a transition-metal center could participate-ideally, catalytically-in some reaction(s) leading to main-group metal-alkyl bond cleavage a t much lower temperatures. At first glance, there are countless reactions wherein a transition-metal center brings about main-group metal-alkyl bond cleavage, but nearly all are alkyl/halide or alkyl/(alk)oxide exchange, as in eq 1. As a potential source of main-group metal MR
-
+ M'X
MX
+ M'R
(1)
X = halogen, M = main-group metal compound, R = alkyl, M' = transition-metal compound atoms, this reaction is self-defeating, since the halo/alkoxide groups are more difficult t o remove from the main-group metal atom than are alkyl groups. A more promising reaction is bimolecular elimination; in one manifestation of this reaction type an active hydrogen atom participates in the elimination of alkane (eq 2).2a (In the case MR
+ M'H
-,MM'
+ RH
(2)
R = alkyl, M = main-group metal compound, M' = transition-metal compound when M' is another main-group atom, e.g. Si, P, As, S, instead of a transition-metal center, this reaction is extremely important in the growth of semiconductor devices, mentioned earlier.1*3s4) ( I ) The literature on this topic is vast. See, for instance: Stringfellow, G. B.; Buchan, N. I.; Larsen, C. A. In Materials Research Society Symposia Proceedings; Hull, R., Gibson, J. M., Smith, D. A,, Eds.; Materials Research Society: Pittsburgh, PA, 1987; Vol. 94, pp 245-253, and other articles in this volume. (2) (a) Tuck, D. G. Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon Press: Oxford, 1982; Vol. 1, Chapter 7, pp 683-723. Boocock, S. K . ; Shore, S. B. Ibid.; Vol. 6, Chapter 41.2, pp 947-981. (b) Clarkson, L. M.; Clegg, W.; Norman, N. C.; Tucker, A. J.; Webster, P. M. Inorg. Chem. 1988, 27, 2653-2660. (3) See: Pitt, C. G.; Purdy, A. P.; Higa, K. T.; Wells, R. L. Organometallics 1986, 5, 1266-1268 and references therein. See also: Cowley, A. H.; Benac, B. L.; Ekerdt. J. G.; Jones, R. A.; Kidd, K. B.; Lee, J. Y . ;Miller, J. E. J . A m . Chem. SOC.1988, 110, 6248-6249. A novel MM' compound prepared, however, by customary nucleophilic reagents is described by: Byrne, E. K.; Parkanyi, L.; Theopold, K. H . Science 1988, 241, 332-334.
0002-7863/89/ 15 1 1-2575$01.50/0
Another promising reaction type is direct bimolecular addition, summarized in eq 3. Literature examples of this third reaction MR
+
LnM'
-
R
I L,M'M
(3)
R = alkyl, M=main-group metal compound LnM'=
transition-metal compound
include the addition of alkyltin5 or -lead5s6compounds to platinum centers and addition of aIkylmercury7~* and the postulated addition of alkylcadmium* compounds to certain other metal centers. In the course of our studies we discovered additional remarkable examples of this reaction type, leading to a family of compounds described herein. Our particular interest was in alkylindium chemistry and we hoped to find some transition-metal compound(s) that could cleave alkyl-indium bonds, a t the same time avoiding the conventional reactions summarized in eq 1 and 2. This required transition-metal compound(s) having no halides or alkoxides and no acidic hydrido hydrogen atoms.2a W e decided to work with electron-rich transition-metal compounds capable (at least in principle) of forming Lewis acid-base adducts with organoindium compounds, reminiscent of the alkylaluminum adducts studied by Mayer and Calabrese in this d e ~ a r t m e n t . ~From earlier work we were familiar with several methyl(trimethylphosphine)iridium compounds that are quite reactive toward a variety of organic substrates,I0 and which might form adducts with organoindium compounds. W e soon found that reactions between methyl(tri(4) Interestingly, conditions that suppress (rather than enhance) this reaction can be advantageous. Moss, R. H.; Evans, J. s.J . Crysf.Growth 1981,
55, 129-134.
(5) Eaborn, C.; Pidcock, A,; Steele, B. R. J . Chem. SOC.,Dalton Trans. 1976, 767-776 and references therein. Eaborn, C.; Kundu, K.; Pidcock, A. Ibid. 1981, 1223-1232. AI-Allaf, T. A. K.; Eaborn, C.; Kundu, K.; Pidcock, A. J . Chem. Soc., Chem. Commun. 1981, 55-56. AI-Allaf, T. A. K.; Butler, G.; Eaborn, C.; Pidcock, A. J . Organomet. Chem. 1980, 188, 335-343. (6) Jawad, J. K; Puddephatt, R. J. Inorg. Chim. Acta 1978, 31, L391L392. (7) One remarkable example of R2Hg addition was reported by: Clark, G. R.; Hoskins, S. V.; Roper, W. R. J . Organomet. Chem. 1982, 234, C 9 C 1 2 . (8) Razuvaev, G. A,; Latyaeva, V. N.; Vishinskaya, L. 1.; Cherkasov, V. K.; Korneva, S. P.; Spiridonova, N. N. J . Organomet. Chem. 1977, 129, 169-174. Use of R2Cd, R,Hg addition in syntheses of novel transition-metal compounds is described by: Roper, W. R. Ibid. 1986, 300, 167-190. (9) Mayer, J. M.; Calabrese, J. C. Organometallics 1984, 3, 1292-1298 and references therein. ( I O ) (a) Thorn, D. L. Organometnllics 1982, I , 197-204; J . Mol. Catal. 1982, 17, 279-288. (b) Thorn, D. L.; Tulip, T. H . J . Am. Chem. Soc. 1981, 103, 5984-5986. (c) Calabrese, J. C.; Colton, M. C.; Herskovitz, T.; Klabunde, U.; Parshall, G . W.; Thorn, D. L.; Tulip, T. H . Anr. N.Y. Acad. Sci. 1983, 415, 302-313. (d) Tulip, T. H.; Thorn, D. L., unpublished work. (e) Thorn, D. L. Organometallics 1986, 5, 1897-1903.
0 1989 American Chemical Society
J . A m . Chem. Soc., Vol. 111. No. 7 , 1989
2516
Thorn and Harlow
methylphosphine)iridium( I) and alkylindium compounds do occur, rapidly and reasonably cleanly under appropriate conditions, but the reactions involve actual alkyl-indium bond cleavage instead of Lewis acid-base adduct formation.
133
63 I
C32
Results The first reactions attempted were between BrInMe, and MeIr(1) substrates. In tetrahydrofuran solution a t room temperature the reaction between BrInMe, and IrMe(PMe,), forms a mixture of two products, characterized as the mer and fuc isomers of Ir(Me),(InMeBr)(PMe,), (compounds 1,2; eq 4). Me
I / I
/
M e T i r -
InMeBr
1 1rMe(PMe3),
+
BrInMe2
t ether
‘1
pyridine (slow)
(4)
, I Me - I r -I n M e B r I‘ 2
Reasonably pure samples of the separate isomers can be obtained by using different solvents. When the reagents are combined in benzene, mer compound 1 precipitates. Redissolved in pyridine, its initial N M R spectrum is quite unambiguous for a compound having two inequivalent IrCH, groups and one InCH, group. But on standing in pyridine solution compound 1 slowly isomerizes to thefac isomer 2, with two chemically equivalent IrCH, groups. Combining Ir(CH3)(PMe3), and BrInMe, in ether causes fuc compound 2 to precipitate, and in pyridine solution 2 slowly isomerizes to the same mixture of mer and fuc compounds. Evidently an equilibrium is established between mer and fuc compounds, favoring the fuc isomer in solution a t room temperature. Upon finding that (trimethylphosphine)methyliridium(I)compounds add the In-CH, bond of BrInMe, in preference to the In-Br bond, we tried the reactions of MeIr(1) compounds with InMe3. In benzene or alkane solution both IrMe(PMe,), and IrMe(C2H4)(PMe3), react rapidly with InMe,-ether to form mixtures offac- and mer-IrMe,(InMe2)(PMe3),, compounds 3 and 4 (eq 5 ) , in essentially quantitative in situ yield. After drying in vacuo (to remove ether, PMe,, and any excess InMe,) the material can be recrystallized, with poor recovery, from warm pentane solution. Both the crude reaction mixtures and the recrystallized material consist primarily of thefuc isomer 3 with ca. 15% of the mer isomer 4. Distinct N M R signals are seen for all methyl groups of both isomers, except for the InMe, groups, which display only a single peak (somewhat broad) a t room temperature. The position of this peak varies from sample to sample, probably owing to rapid I n / M e exchange among compounds 3 and 4 and traces of excess InMe,. Thefac-mer mixture apparently comprises a n equilibrium mixture, like the BrInMe, adducts 1 and 2. Ethylene reversibly displaces InMe3 from compounds 3 and 4, establishing an equilibrium with the compound Ir(Me)(C2H4)(PMe3),(eq 5 ) . Reversible loss of InMe, Me I
c11
Figure 1. Perspective drawing of IrH(Et)(EtJn)(PMe,),. ellipsoids are drawn at the 50% probability level.
Me
Thermal
form compounds 3 and 4 with a completely statistically scrambled 13CH3population. While the remaining InCH, groups of compounds 3 and 4 may be exchanging on the N M R time scale, they are unreactive toward methyliridium(I), and mixtures of 3 and 4 with either IrMe(PMe3), or IrMe(C,H,)(PMe,), are stable for several days a t room temperature. Other organoiridium(1) compounds react with InMe, but form complex mixtures of products that have not been completely characterized. For instance, the reaction between IrH(PMe,), and InMe, results in several compounds, some containing IrH and IrCH, groups ( N M R ) . Likewise, 1r@-MeC,H4)(PMe3), forms several products with InMe,, some containing IrCH, groups. Alkyl/aryl redistribution reactions may be occurring. IrCI(C,H,,)(PMe,),” and InMe, react in benzene to form a merIrMe, compound, most likely the chloro analogue of 1 formed in a chloro/methyl redistribution sequence (eq 6). Ct
Me Me-Ir-
I/
InClMe
(6)
I‘ InEt3 is also quite reactive toward the iridium compounds used in this study. InEt, and Ir(Me)(PMe,), react rapidly to form a mixture of several compounds, the most readily identifiable being ethylene and Ir(Me)(C2H4)(PMe3),. Two hydridoiridium compounds are present, IrH(PMe,), and a new compound, which we (5) (see below). have identified as IrH(C2H,)(In(C2H5)2)(PMe3)3 A scheme to account for these products is presented in eq 7. In PMeg
Me
I
-I
Et
PMe3
InMeEt2
r -I n E t 2
IrEt(PMeg),
Me InEt3
PMe3
3 H
Me
I
,I‘
Me-Ir-InMez
I‘
CZH 4
L__ I r M e ( C 2 H 4 ) ( P M e 3 ) 3
+
InMeg
(5)
-C2H4
4
from compounds 3 and 4 also allows 13CH3scrambling between iridium and indium: Ir(13CH3)(PMe3)4 and In(I2CH,), react to
-1r
Et
I /- 1 n E t z
‘I 6 (1 I ) Herskovitz, T.Inorg. Synrh. 1982, 21, 99-103 and references therein.
this scheme, compound 5 arises from a reaction between InEt3 and IrH(PMe3)4. Separate experiments verified this reaction and provided single crystals of compound 5, used for the X-ray structure determination (see Figure I ) . Discussion Our initial expectation was that reactions involving the Inalkyl bond would be most easily detected via the observation of alkyl exchange between indium and the transition-metal substrate (case A or Bi of ref 6). This proved to be wrong, and the oxidative addition of the In-alkyl bond to iridium(1) compounds was immediately revealed in the reaction between BrInMe2 and IrMe4). Given that the Br-In bond of BrInMe2 is readily (PMe,), (aionized, we had expected an oxidative or ionic addition of (Br-)(InMe2+)12 to Ir(1). While this may happen a t intermediate stages of the reaction, in the observed products it is only the In-alkyl bond that has been added to Ir(1). The propensity of transition-metal compounds to add a main-group metal-alkyl or -aryl bond in preference to a main-group metal-halo bond is already established for reactions between mixed organohalotin and -lead compounds and certain Pt(0) and Pt(I1) compound^.^ But certain other Pt(0) and Pt(I1) compounds do add the halometal bond of alkylhalosilicon, -germanium, -tin, and -lead comp o u n d ~ . ' ~These addition reactions are probably controlled by a delicate thermodynamic balance of energies of metal-alkyl and metal-halo compounds; it is unlikely that there are kinetic constraints in the iridium system, given the lability of the InMe, adducts and the interconvertibility of mer andfac isomers 1 and 2. Realizing that In-CH3 bonds are thermodynamically favored to add to Ir(I), we naturally devoted most of our effort to studying the reaction chemistry of trialkylindium compounds. The most straightforward reaction of InMe, is with IrMe(PMe3),, which makes an equilibrium mixture offac- and mer-IrMez(InMe2)(PMe3)3isomers 3 and 4 (eq 5 ) . This addition is reversible, and InMe, can be displaced from 3 and 4 by adding PMe,. Likewise, excess ethylene reversibly displaces InMe, from 3 and 4 to form IrMe(C2H4)(PMe3),;in an open reaction vessel under an inert atmosphere ethylene is released, and the mixture of compounds 3 and 4 is reestablished. A complication is that InMe, forms adducts with any Lewis base, including PMe, and diethyl ether, and the presence of these Lewis bases can shift the equilibrium between compounds 3 and 4 and InMe3-base. In fact we were initially a t pains to prepare InMe3 free from ether, and IrMe(olefin)(PMe,), compounds free from labile phosphine, in order to prevent competition by Lewis base adduct chemistry of InMe,. But these precautions proved unnecessary as equilibrium positions favor the iridium-alkylindium products and competing phosphine or ether is easily removed. While the exact mechanism of the In-CH3 bond addition has not been established, an extremely plausible scheme is shown in eq 8. Here, the initial step is InMe3 coordination to the basic, electron-rich MeIr( 1 ) species, forming an adduct familiar from (or in concert with) the work of Mayer and C a l a b r e ~ e .Following ~ rearrangement of the phosphine ligands, a methyl group migrates from the indium atom to the iridium atom, where the indium center mimics a carbon center in the reverse of the well-known alkyl alkylidene/carbene migration r e a c t i ~ n . ' ~ If ~ ~these ~J~ steps are general and reversible, the chemistry observed in this study can be accounted for.
-
(12) Hausen, H. D.; Mertz, K.; Weidlein, J.; Schwarz, W. J . Orgunornet. Chem. 1975, 93, 291-296. (13) Kuyper, J. Inorg. Chem. 1977,16, 2171-2176. Ibid.1978,17,77-81.
Ibid. 1978, 17, 1458-1463. Yamashita, H.; Hayashi, T.; Kobayashi, T.; Tanaka, M.; Goto, M. J . Am. Chem. SOC.1988, 110, 4417-4418. (14) Sharp, P. R.; Schrock, R. R. J. Organomet. Chem. 1979,171,43-51. Hayes, J. C.; Pearson, G . D. N.; Cooper, N.J. J. Am. Chem. Sor. 1981,103, 4648-4650. Hayes, J. C.; Cooper, N. J. Ibid. 1982, 104,5570-5572. Jernakoff, P.; Cooper, N. J. Ibid.1984, 106, 3026-3027. Werner, H.; Kletzin, H.; Hoehn, A.; Paul, W.; Knaup, W.; Ziegler, M. L.; Serhadli, 0. J . Orgunomet. Chem. 1986,306, 227-239 and references therein. For an interestipg example of alkyl shift from Pb to a transition metal, see: Pannell, K. H. J. Orgunornet. Chem. 1980, 198, 37-40.
2517
J . Am. Chem. SOC.,Vol. I I I , No. 7 , I989
Transition Metal-Organoindium Chemistry Me
Me
Me
I
/
Me
-I r - I n - M e
/I cn3
\Me
migrate
it
/
/ / CHa migrate
Me
1 /Me/Me
-1r-In
'I
\Me
3
/
Me
Me -I r - I n -
Me
'Me
1'
Me Me-Ir
I /-In
'1
/
Me
\Me
4
The reaction between InMe, and other iridium substrates is much less straightforward. IrH(PMe,), and InMe, react rapidly, forming a complicated mixture of several products. The ' H N M R spectrum contains resonances of new hydrido and methyl compounds, possibly including IrH(Me)(InMe2)(PMe3), (analogous to compounds 3 and 4), but positive identification has not been made. Fortunately, the reaction between InEt, and IrH(PMe3), is considerably cleaner (see below). Adding an In-CH, bond to a transition-metal complex, especially a transition-metal complex that binds methyl groups even more strongly than does indium, does not necessarily "activate" the indium entity toward further reaction. There is no a priori reason that alkyl groups are more easily removed from 3 and 4 than from InMe, itself. Our hope was to identify new reactions that do remove indium or iridium methyl groups from 3 and 4, but here we have had no great success: All reactions we tried with compounds 3 and 4 (e.g. hydrogenolysis, aldehyde addition, alkyl halide addition) appeared to involve only the Ir(Me)(PMe,), and/or InMe, formed by reversible loss of InMe, from 3 and 4. This is not surprising, as iridium tends to form very stable methyl and hydridomethyl compounds from which methane is evolved only under relatively drastic conditions. However, ethyl compounds of many transition metals are unstable, tending to lose ethylene by p elimination. Therefore, we explored some reactions of Ir compounds with InEt,, looking for addition of In-Et bonds and subsequent p elimination. The reaction between InEt, and IrMe(PMe,), forms a mixture of compounds. Evidently, there are several separate reactions occurring among several different species, as outlined in eq 7. The most probable initial reaction between IrMe(PMe3), and InEt,, adding an In-Et bond to iridium, is entirely analogous to the InMe, reaction of eq 5. Reversible addition of alkyliridium bonds allows exchange between methyl and ethyl groups, and the resulting ethyl compound Ir(C,H,)(PMe,), decomposes to IrH(PMe,), and C2H4.10C,dThe liberated ethylene in turn reacts rapidly with IrMe(PMe,), to form IrMe(C2H,)(PMe3)3.10b,dThe hydrido compound IrH(PMe3), has been shown in separate experiments to react readily with alkylindium compounds, intractibly with InMe, (see above) but forming primarily one compound with InEt,. This compound has been identified as Ir(H)(C2Hs)(InEt,)(PMe,), ( 5 ) , based on its ' H and I3C N M R spectra, its reversible reaction with PMe, to restore IrH(PMe3), and InEt,, and its structure as determined by X-ray diffraction (see below). PMe,, liberated in the course of the reaction, tends to bind to trialkylindium, displace ethylene from IrMe(C,H,)(PMe,),, and provide additional equilibria that further complicate the overall reaction scheme. As an extension of this work, we looked briefly a t reactions between alkylindium and selected platinum compounds. The Pt(0) compound Pt(C,H,)(PPh,), reacts with InMe,, releasing ethylene and forming a methylplatinum compound, the N M R spectrum of which is suggestive of PtMe(1nMe2)(PPh3),, but the compound decomposes readily. PtMe2(bpy)6,'3reacl; with InMe, reversibly
2518
J . Am. Chem. SOC.,Vol. 111, No. 7, 1989
Table 1. Interatomic Distances Ir-In 2.601 (1) Ir-P1 2.275 (2) Ir-P2 2.302 (2) Ir-P3 2.309 (2) 2.192 ( 7 j Ir-Cl 1.57 Ir-HIr 2.211 (9) In-C3 2.179 (10) In-C5 1.821 (8) P1-c11 1.820 (8) P1-c12
(A) P1-C13 P2-C2 1 P2-C22 P2-C23 P3-C3 1 P3-C32 P3-C33 Cl-C2 c3-c4 C5-C6
1.839 (9) 1.814 (8) 1.812 (8) 1.817 (9) 1.833 (9) 1.827 (9) 1.800 (8) 1.438 (12) 1.474 (14) 1.290 (16)
to form a compound whose IH N M R spectrum is consistent with Pt(Me),(bpy)(InMe,). N M R spectra of mixtures of InMe, and PtMe,(PMe,), or PtMe,(P(tol),), show only minute shifts, suggesting that an adduct may form reversibly but is not thermodynamically favored. With InEt,, Pt(Me),(1,5-C8HI2) reacts slowly to form some methylindium compound(s) and Pt(Et),( 1,5-C8HI2).(Likewise, Pt(Et),( 1 ,5-C8HI2)and InMe, form Pt(Me),( 1,5-C8H,,) and ethylindium compounds.) For other platinum compounds PtMe2(bpy) and PtMe2(PMeJ2, there is significant methyl/ethyl exchange between Pt and InEt,, although we have not characterized the species present. Also, in each case there is only a small amount of ethylene formed, consistent with the tendency for platinum ethyl groups to undergo rapid @ elimination only at elevated temperatures.15 We also looked very briefly at reactions of rhodium compounds with InMe, and of AlMe3l6and ZnMe, with iridium and platinum compounds. ZnMe, reacted with IrMe(PMe,), to form thefac isomer of Ir(Me),(ZnMe)(PMe,), (6),but scouting reactions of ZnMe, with Pt(C,H,)(PPh,),, Pt(Me),(bpy), and Pt(Me),(PMe,), were intractible and were not pursued further. Mixtures of AlMe, and Ir(Me)(PMe,), in benzene did not form an identifiable adduct, but there were significant shifts in the N M R signals, strongly suggestive of rapid exchange among species such as Ir(Me),(AIMe,)(PMe,),, AIMe,PMe3, and/or Ir(Me)(PMe3),AIMe3. Rh(Me)(PMe,), and InMe, likewise did not form an isolable adduct but did show evidence for reversible adduct formation in solution, with an N M R spectrum nearly identical with that of Ir‘(Me)(PMe,),-AIMe, mixtures. R h H ( P i ~ f e , )and ~ InMe, reacted immediately, liberating methane, but no other compound could be identified in the resulting complicated mixture. Structure of Compound 5. Compound 5 is the first crystallographically characterized compound with an In-Ir bond and a rare example of a sterically noncongested 3-coordinate organoindium species.” A perspective drawing of the compound is in Figure I and bond distances and angles are in Tables I and 11. Coordination about the iridium center is essentially octahedral, as expected for 6-coordinate trivalent iridium. The hydrido hydrogen atom was located, but its position was not refined. Coordination about the indium atom is effectively planar and trigonal, although C1 of the iridium ethyl group is moderately close (3.040 (8) A). Bond angles about indium are considerably distorted from 120’, in particular C3-In-C5 (104.1 (4)’). This contrasts with C,Hs(CO),WGaMe2, the most closely related compound in the literature, which has angles about the gallium atom very close to 12Oo.l8 Simplistically, the InEt, entity of compound 5 resembles inEt,- (isoelectronic with strongly bent stannylene compoundsig) more than it resembles InEt,’ (linear like InMe2+I2 (15) McCarthy, T. J.; Nuzzo, R. G.; Whitesides, G. M. J . A m . Chem. SOC. 1981, 103, 3396-3403 and references therein. ( 1 6) Alkylrhodium and -iridium ‘adducts” of methylaluminum have been
observed in the reaction of chloro compounds with trimethylaluminum: Vizquez de Miguel, A.; Gbmez, M.; Isobe, K.; Taylor, B. F.; Mann, B. E.; Maitlis, P. M. Organometallics 1983, 2, 1724-1730. Isobe, K.; Vizquez de Miguel, A,; Nutton, A,; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1984, 929-933. Trialkylaluminum compounds have been found to bind to coordinated ethylene in Nb, Ta compounds: McDade, C.; Gibson, V. C.; Santarsiero, B. D.; Bercaw, J . E. Organometallics 1988, 7, 1-7. (17) Carty, A. J.; Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.; Singh, A.; Taylor, N. J. Inorg. Chem. 1980, 19, 3637-3641. (18) St. Denis, J. N.; Butler, W.; Glick, M. D.; Oliver, J. P.J . Organomet. Chem. 1977, 129, 1-16.
Thorn and Harlow Table 11. Intramolecular Angles (deg) In-Ir-P1 92.85 (5) Ir-PI-C13 In-Ir-P2 160.41 (6) Ir-P2-C21 In-Ir-P3 93.64 (5) Ir-P2-C22 In-Ir-C1 78.2 (2) Ir-P2-C23 In-Ir-HIr 79 Ir-P3-C31 Pl-Ir-P2 98.02 (7) Ir-P3-C32 Pl-Ir-P3 97.64 (7) Ir-P3-C33 P2-Ir-P3 100.95 (7) C1 l-Pl-Cl2 P1-Ir-C1 167.6 (2) C1 l-Pl-Cl3 P2-Ir-C1 88.3 (2) C12-Pl-Cl3 P3-Ir-C1 91.5 (2) C21-P2-C22 P1-Ir-HIr 90 C21-P2-C23 P2-Ir-HIr 85 C22-P2-C23 P3-Ir-HIr 170 C31-P3-C32 C1-Ir-HIr 80 C31-P3-C33 Ir-In-C3 124.0 (2) C32-P3-C33 Ir-In-C5 131.8 (3) Ir-Cl-C2 C3-In-C5 104.1 (4) In-C3-C4 Ir-P1-Cll 115.2 (3) In-C5-C6 Ir-P1-C12 123.3 (3)
116.9 (3) 117.4 (3) 119.8 (3) 115.3 (3) 117.7 (3) 119.0 (3) 117.0 (3) 100.5 (4) 98.8 (4) 98.1 (4) 101.0 (4) 100.3 (4) 99.9 (5) 99.2 (4) 100.5 (4) 99.9 (4) 120.0 (6) 118.0 (6) 122 (1)
-
and isoelectronic R,Hg compounds). Then bonding in 5 could be described as “(H)(Et)Ir(III)+ InEt,”, consistent with the assignment of +3 as the formal oxidation state of iridium. Compounds having transition metal-indium bonds are wellbut known,2 including compounds with Rh-In or Ir-In structures have not been reported for the latter. Without other Ir-In bond lengths for comparison, we cannot say how important T back-bonding might be in determining the Ir-In bond distance (2.601 (1) A). We note that large thermal motion of the atoms of this low-melting compound may artificially shorten calculated bond lengths, especially C5-C6 (see the Experimental Section). We also cannot say how important C-In interaction with the iridium ethyl group might be. The orientation of the diethylindium group allows maximum interaction with the iridium ethyl group, and the C1-Ir-In angle (78.2 (2)’) is consistent with some attractive interaction. But note that the far-triphosphine arrangement is rather crowded and P-Ir-P angles approach loo’, so angles among the remaining ligands (H, Et, InEt,) approach 80’ regardless of any incipient bonding interaction. The orientation of the diethylindium group might simply be a steric preference for eclipsing the relatively small Ir-H group. Likewise, the C-C bond of the iridium ethyl group eclipses the metal-hydride bond, as i n the related hydridoethyl compound (PMe3)4Ru(H)(C,H,).23 Summary and Conclusions One aspect of our original interest has been addressed, and we now know that alkyl-indium bond cleavage can be achieved under very mild conditions using transition-metal compounds. With organoiridium compounds the predominant reaction is direct “oxidative addition” of the alkyl-indium bond. The reactions are reversible, and trialkylindium can be displaced from the iridium compound by adding ligands (PMe,, C2H4) that bind to iridium (and, to some extent, trialkylindium). In the case of organoplatinum compounds, such addition reactions tend to be less favored, and adducts are observed only in certain cases. However, the addition products readily undergo exchange reactions with alkyl groups already present in the iridium or platinum substrate, allowing further sequences of reactions that can become complicated (e.g. eq 7). Other main-group alkyl compounds react similarly with organoiridium and -platinum compounds, as already reported in the literature and as we have observed for dimethylzinc. (19) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J . Chem. Soc., Dalfon Trans. 1976, 2268-2274. Cotton, J. D.; Davidson, P. J.; Lappert, M. F. Ibid. 1976, 2275-2286. Lappert, M. F.; Miles, S . J.; Power, P. P.;Carty, A. J.; Taylor, N. J. J . Chem. SOC.,Chem. Commun. 1977, 458-459. (20) Jones, N. L.; Carroll, P. J.; Wayland, B. B. Organomefa/lics 1986, 5, 33-37. (21) Hsieh, A. T. T.; Mays, M. J . Inorg. Nucl. Chem. Lett. 1971, 7, 223-225. (22) Fagan, P. J., personal communication. (23) Wong, W.-K.; Chiu, K. W.; Statler, J. A,; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. Polyhedron 1984, 3, 1255-1265.
J . A m . Chem. SOC.,Vol. 111, No. 7 , 1989 2519
Transition Metal-Organoindium Chemistry Table 111. ' H N M R Data' for Methyl Compounds comud (solvent)
mer-Ir(Me)2(InMeBr)(PMe3)3 1 (PY-4) fac-Ir( Me)z(InMeBr) (PMe,), 2 (PY-4) fac-Ir( Me),(InMez)(PMe3)3 3 (C6D6)
mer-Ir(Me)z(InMe,)(PMe3)3 (C6D6)
fa~-Ir(Me),(ZnMe)(PMe~)~ 6 (CADI)
PMe,
IrMe
1.42 (18 H , t, 3.2) 1.48 (9 H , d, 7.7) 1.10 (9 H , d, 7.5) 1.53 (18 H , d, 7.5) 0.90 (9 H , d, 7.0) 1.14 (18 H , d, 6.8) 1.10 (18 H . t. 2.9) 1.13 (9 H , d, 7 . 4 ) 0.93 (9 H , d, 6.2) 1.22 (18 H . d, 6.2)
-0.11 (3 H , q, 6.7) +0.06 (3 H , t, 8.1, of d, 4.6) +0.14 (6 H , d, 11.5, of q, 3.2)
(In,Zn)Me
0.42 (3 H , d, 1.5)
+0.12 (6 H , d, 11.9, of q, 3.5)
0.38 (6 H , s)*
-0.11 ( 3 H . d. 6.9. o f t . 6.0) +0.25 (3 H , t, 8.2, of d, 4.6) +0.40 (6 H , d, 13.1, of q, 3.5)
0.38 ( s ) ~
0.30 (3 H , s)
0.04 (3 H , s)
"Chemical shifts in ppm downfield from external Me4Si. Coupling constants in hertz. bSignal can appear at 0.03 if traces of excess InMe3-ether are present.
Experimental Section
Table IV. Crystal and Refinement Data for Compound 5 Owing to the extremely air- and moisture-sensitive nature of maingroup metal alkyl and alkyliridium(1) compounds, all compounds were prepared, stored, and handled under an inert atmosphere, generally in 623.45 formula wt a glovebox under nitrogen. Note particularly that alkylindium, alkyl14.836 (3) a, A aluminum, and alkylzinc compounds are pyrophoric in air and evolve 14.658 (3) b, A flammable gases when exposed to moisture. Solvents were dried using 11.022 (2) c, A standard methods. Triethylindium, trimethylaluminum, and dialkylzinc 90.22 ( I ) & deg compounds were obtained commercially. Methyltetrakis(trimethy1v,A3 2396.9 phosphine)iridium and -rhodium were prepared as in previous ~ o r k ; ' ~ , ~ ~ 4 trimethylindium, bromodimethylindium, trimethylindium etherate,25and P2,/n (No. 14) space gP platinum compounds26'28 were prepared by modifications of literature 1.727 d c a l c ) , g/cm3 methods. Ambient-temperature N M R spectra were obtained with GE cryst dimens, mm 0.36 X 0.30 X 0.50 QE-300 instruments. ' H N M R data for iridium methyl compounds are temp, " C -100 presented in Table 111. radiatn Mo K a from graphite monochromator (Bromomethylindium)dimethyltris(trimethylphosphine)iridium(III). IJ, cm-' 66.66 mer isomer 1: A mixture of 0.04 g of BrInMez and 0.095 g of IrMetotal no. of reflctn 3614 unique with I > 3u (PMe3), in benzene was stirred for 30 min and filtered, collecting 0.01 final no. of variables 181 g of white solid (an impure mixture of compounds 1 and 2 by ' H N M R ) . R 0.034 The filtered solution slowly deposited additional solid, which was collected 0.033 Rw after 90 min; estimated yield 0.02 g of pure mer compound 1 ('H N M R , error of fit 1.19 py-d5; see Table 111). fac isomer 2: The reagents were combined in ether, and 0.07 g of white powder was collected after 30 min (57% of purefac isomer by ' H Table V. Fractional Coordinates ( X IOOOO) and Isotropic Thermal N M R , py-dS). In pyridine solution each compound slowly isomerized, Parameters after 2 days reaching an equilibrium mixture of compounds 1 (25%) and atom X Y Bk" 2 (75%). (Dimethylindium)dimethyltris(trimethylphosphine)iridium(III). fac Ir 1410.7 (2) 2226.6 (2) 2523.4 (2) 2.4 (1)' and mer isomers (3,4): IrMe(PMe,), (0.027 g) and InMe3-ether (0.010 In 1581.3 (5) 2480.2 (4) 200.4 (5) 4.2 (1)' g) were combined in 1 mL of C6D6. Compounds 3 and 4, PMe3, and PI 252 (1) 1226 (1) 2274 (2) 3.3 (1)' ether were the only species present ( ' H N M R ) . The solution was P2 1768 (1) I871 (1) 4502 (2) 3.3 ( I ) ' evaporated, and the residue was redissolved in warm pentane and cooled P3 557 (1) 3528 (1) 3.5 (1)' 2792 (2) to -30 OC. After 1 day 0.02 g of flaky white solid was collected. When C1 2657 (5) 3027 (5) 4.4 (2)' 2438 (8) redissolved in C6D6, the material was entirely compounds 3 (88%) and C2 3498 (7) 2584 (7) 8.9 (5)' 2171 (14) 4 (12%) by, ' H N M R (Table 111). After bubbling ethylene through the C3 2129 (7) 1449 (7) -1062 (8) 6.5 (3)' solution briefly, the ' H N M R spectrum revealed the presence of signifC4 2461 (7) 583 (7) -548 (9) 6.2 (3)' icant amounts (ca. 40%) of the ethylene adduct IrMe(C,H,)(PMe3)310b*d C5 1338 (12) 3669 (7) -941 (10) 10.4 (5)' and "free" InMe3. Allowing ethylene to dissipate into a nitrogen atmoC6 932 (13) 3605 (9) -1975 (11) 13.7 (7)' sphere restored compounds 3 and 4. 2497 (8) 4.4 (2)' c11 543 (5) 31 (5) (Diethylindium)ethylhydridotris(trimethylphosphine)iridium(III) ( 5 ) . C12 -793 (5) 1291 (6) 3130 (9) 5.8 (3)' IrH(PMe3)>9 (0.10 g) and InEt3 (0.04 g) were dissolved in benzene. C13 -244 (6) 1143 (6) 746 (9) 5.1 (3)' After standing 10 min at roam temperature, the solution was evaporated, C21 2352 (6) 2732 (6) 5387 (7) 5.6 (3)' and the oily residue was dried (lo-) Torr, 30 min) and redissolved in ca. C22 884 (6) 1541 (6) 5545 (7) 5.3 (3)' 0.5 mL of pentane. Refrigeration at -30 OC for 2 days produced 0.025 C23 2533 (7) 914 (6) 4695 (8) 5.9 (3)' g of pale yellow, transparent crystals that melted when warmed to room C31 -413 (6) 3699 (6) 1781 (9) 6.1 (3)' temperature. Crystallized material was used for the reported N M R data, 4 (6) 3715 (6) 4249 (9) 5.7 (3)' C32 but N M R spectra of crude reaction mixtures were quite similar. 'H C33 1125 (6) 4605 (5) 2621 (9) 5.6 (3)' N M R of 5 (C&, chemical shifts in ppm downfield from external Me,Si, HIr 2102 1454 2196 4.0 multiplicities and coupling constants (Hz) in parentheses) H I r , -1 1.6 [d (123) o f t (1711; (H3C)3P, 1.16 (d, 7 . 9 , 1.17 (d, 7.3), 1.25 (d, 7.4); ethyl restored IrH(PMe3), and IhEt3.xPMe3. H , 1.1 (br m), 1.3 (br m), 1.86 (br, pseudo q, 8). ('H)I3C N M R of 5: (Methylzinc)dimethyltris(trimethylphosphine)iridium(III) (6). IrMeIrCHz, -22.11 [d (64.4) o f t (6.3)]; IrCHzCH3,30.19 (d, 13.2); InCHz, (PMe3)4 (0.050 g) and Me2Zn (0.012 g) were combined in C6D,. The 18.92 (d, 21.9); InCH,CH3, 12.80 (s); P(CH3)3, 21.75 (d, 23.2), 22.75 N M R spectrum showed essentially quantitative formation of 6, but the (d, 25.9), 28.46 (d, 20.8). Treating solutions of compound 5 with PMe, MeZn signal was very broad. The solution was evaporated and the residue redissolved in C6D6; the ' H N M R signals were then much (24) Jones, R. A.; Mayor Real, F.; Wilkinson, G.; Galas, A. M. R.; sharper. Very small amounts, ca. 5%, of a second compound could be Hursthouse, M. B.; Malik, K. M. A. J . Chem. SOC.,Dalton Trans. 1980, discerned, N M R signals of which are consistent with a mer isomer of 6. 511-518; 1981, 126-131. Reaction of Trimethylindium with Dimethylbipyridylplatinum(II). (25) Clark, H. C.; Pickard, A. L. J . Organomet. Chem. 1967, 8, 427-434. PtMe,bpy (0.008 g) in C6D6was treated with excess InMe3-ether, im(26) Nagel, U. Chem. Ber. 1982, 115, 1998-1999. mediately depositing a yellow solid. After recrystallization from hot (27) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973,59,411-428. benzene, its ' H N M R spectrum (dilute C6D6) showed unreacted (28) Chaudhury, N.; Puddephatt, R.J. J . Orgunornet. Chem. 1975, 84, 105-1 15. PtMe,bpy (PtMe, chemical shift 1.70) (ca. 33%), PtMe3(InMez)(29) Thorn, D. L.;Tulip, T. H. Organomefallics 1982, I , 1580-1586. (bpy)(PtMe, 0.18, 1.67) (ca. 67%), and InMe, (-0.20).
z
z
2580
J . A m . Chem. SOC.1989, 11 I , 2580-2582
X-ray Structure of Compound 5. Working in a drybox, under a stream of cold (ca. -20 "C) nitrogen gas to prevent melting, a single crystal of compound 5 was loaded into a capillary and sealed with wax. It was quickly transferred to the diffractometer and cooled to -100 OC in a N, stream. Space group, unit cell, and data collection information are provided in Table IV. T h e solution and refinement were uneventful, except for the hydrido hydrogen atom, which tended to refine to an unacceptably short Ir-H separation. This atom was held fixed a t its Fourier difference map position. Remaining hydrogen atoms were placed in idealized locations. Consistent with the low melting point of the material, there is considerable apparent thermal motion of several of the atoms. most notablv C 5 and C 6 of the indium ethvl ErouD. As a result of this thermal anisotropy, the calculated C5-C6 bond distance is unrealistically short (1.29 (2) A), Being suspicious that this might indicate a vinyl group, formed by metal-catalyzed dehydrogenation, we analyzed the remaining crystals from this batch ( ' H N M R , C6D6) but found absolutely no evidence for a vinyl group nor for any compound other than 5 . Final refinement data is included in Table IV. Largest residual
--
density in the final difference Fourier map is 1.42 e/A3 near the indium atom. Bond distances and angles are listed in Tables I and 11. Nonhydrogen atom positions are listed in Table V. Anisotropic thermal (Tables parameters, hydrogen atom positions, a listing of Fobs vs FCaI, 6-8), and a stereodrawing of the unit cell (Figure 2) are available a s supplementary material.
Acknowledgment. T h e c r y s t a l of compound 5 w a s skillfully m o u n t e d b y L. L a r d e a r . We a l s o t h a n k L. A y e r s for t e c h n i c a l assistance and P. Fagan and R. T. Baker for c o m m u n i c a t i n g results prior to publication.
I
Supplementary Material Available: Tables of a n i s o t r o p i c parameters 6, and hydrogen atom parameters (Table 7 ) and a stereodrawing ofthe unit cell (Figure 2) (3 Pages); listing of Fobsvs Fa,,(Table 8) ( 3 pages). Ordering i n f o r m a t i o n is given on any c u r r e n t masthead page.
A Short, Enantioselective Synthesis of (-) -Swainsonine' Richard B. Bennett 111, Jong-Ryoo Choi, Walter D. Montgomery,* and Jin K. Cha* Contribution from the Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235. Received August 2, 1988. Revised Manuscript Received November 17, 1988 Abstract: A practical, enantioselective synthesis of (-)-swainsonine (1) has been achieved in seven steps from 2,3-o-isopropylidene-D-erythrose ( 6 ) . T h e key step involves t h e construction of t h e bicyclic imine 4 by a n intramolecular 1,3 dipolar cycloaddition of azide 5. This study highlights the synthetic utility of the intramolecular 1,3 dipolar cycloaddition of the unactivated olefinic azides in natural product synthesis.
From the fungus Rhizoctonia leguminicola there w a s isolated a toxic indolizidine alkaloid, swainsonine ( l).3 Swainsonine has also been s h o w n t o be present in locoweed (Astragalus lentigi~ O S U S and ~ ~ ) Swainsona c a n e ~ c e n sas , ~ well ~ as in the fungus Metarhizium a n i s ~ p l i a e . The ~ pronounced a-mannosidase inhibitory6 and i m m u n o r e g ~ l a t i v eproperties ~~~ of swainsonine h a v e s t i m u l a t e d considerable interest in biosynthetic* and pharmaco(1) A preliminary account of this work was presented in part at the 16th International Symposium on the Chemistry of Natural Products, Kyoto, Japan, May 29-June 3, 1988 and at the 3rd Chemical Congress of North America, Toronto, Canada, June 1988. (2) Undergraduate Research Participant. (3) (a) Schneider, M. J.; Ungemach, F. S.; Broquist, H . P.; Harris T. M. Tetrahedron 1983,39, 29. (b) Guengerich, F. P.; DiMari, S. J.; Broquist, H . P. J . A m . Chem. SOC.1973, 95, 2055. (4) (a) Molyneux, R. J.; James, L. F. Science (Washington, D.C.) 1982, 216, 190. Davis, D.; Schwarz, P.; Hernandez, T.; Mitchell, M.; Warnock, B.; Elbein, A. D. Plan1 Physiol. 1984, 76, 972. (b) Colegate, S. M.; Dorling, P. R.; Huxtable, C. R. Aust. J . Chem. 1979, 32, 2257. (c) Skelton, 8 . W.; White, A. H. Aust. J . Chem. 1980, 33, 435. (5) Hino, M.; Nakayama, 0.; Tsurumi, Y . ; Adachi, K.; Shibata, T.; Terano, H.; Kohsaka, M.; Aoki, H.; Imanaka, H. J . Antibiot. 1985, 38, 926. (6) (a) Dorling, P. R.; Huxtable, C. R.; Colegate, S. M. Biochem. J . 1980, 191, 649. (b) Elbein, A. D.; Solf, R.; Dorling, P. R.; Vosbeck, K. Proc. Natl. Acad. Sci. U.S.A. 1981, 78, 7393. (c) Tulsiani, D. R. P.; Harris, T. M.; Touster, 0.J . Biol. Chem. 1982, 257, 7936. (d) Segal, H . L.; Winkler, J. R. Curr. Top. Cell Regul. 1984, 24, 229. (e) Elbein, A. D. CRC Crit. Rev. Biochem. 1984, 16, 21. (f) Winkler, J. R.; Segal, H . L. J . Biol. Chem. 1984, 259, 15369. (g) Segal, H . L.; Winkler, J. R. Prog. Clin. Biol. Res. 1985, 180, 491. (h) Foddy, L.; Feeney, J.; Hughes, R. C. Biochem. J . 1986, 233, 697. (i) McLawhon, R. W.; Berry-Kravis, E.; Dawson, G. Biochem. Biophys. Res. Commun. 1986, 134, 1387. fj)Tulsiani, D. R. P.; Touster, 0. J . Biol. Chem. 1987, 262, 6506. (k) Tropea, J. E.; Swank, R. T.; Segal, H . L. J . Biol. Chem. 1988, 263, 4309. (7) (a) Kino, T.; Inamura, N.; Nakahara, K.; Kiyoto, S.; Goto, T.; Terano, H.; Kohsaka, M.; Aoki, H.; Imanaka, H . J . Anribiot. 1985, 38, 936. (b) Humphries, M. J.; Matsumoto, K.; White, S. L.; Olden, K. Proc. N a f l .Acad. Sci. U . S . A . 1986, 83, 1752. (c) Dennis, J. W. Cancer Res. 1986, 46, 5131. (d) Granato, D. A,; Neeser, J. R. Mol. Immunol. 1987, 24, 849. (e) White, S. L.; Schweitzer, K.; Humphries, M. J.; Olden, K. Biochem. Biophys. Res. Commun. 1988. 150. 615. ( 0 HumDhries. M. J.: Matsumoto.. K.:. White. S. L.; Molyneus, R. J.;'Olden,~K. Can'cer Res. 1988, 48, 1410. (8) Harris, C.M.; Schneider, M , J,; ungemach, F. s,; ill, J , E,; ~ ~ T. M. J . A m . Chem. SOC.1988, 1 IO, 940, and references cited therein. 0 0 0 2 - 7 8 6 3 / 8 9 / 15 1 1 - 2 5 8 0 $ 0 l . 5 0 / 0
Scheme I
1
R=H
2
R=C(CH&
0
3
n
8 R, =Tr r-
L
I
12
1
I I
1
_J
I I R2=H
'Reagents and conditions: (a) Br-Ph3P*CH2CH2CH2C02Et, KN(TMS)2, T H F , -78 OC; (b) p-TsCI, Et3N, CH2C12; (c) NaN,, D M F , 70 100 OC; (d) K2C03, aqueous M e O H , room temperature; (e) toluene, reflux; (f) BH,, THF/H,O,-NaOH; (g) 6 N HCI, T H F .
-
~logical9 ~ studies, i a n ~d its total , synthesis h a s been achieved by Several groups.10 As d e m a n d for swainsonine in cancer research r e m a i n s
0 1 9 8 9 A m e r i c a n C h e m i c a l Society
